1. Field of the Invention
This invention relates to an electronic image pickup apparatus and an electronic image pickup method that utilize a color image pickup element and, more particularly, it relates to an electronic image pickup apparatus capable of picking up a still image and displaying a live view by utilizing a color image pickup element and also to an electronic image pickup method to be used for such an apparatus.
2. Description of the Related Art
Some known electronic image pickup apparatus such as digital still cameras (to be simply referred to as cameras if appropriate) are equipped with a color image pickup element having a plurality of different drive modes. For example, digital still cameras have a drive mode for picking up a still image and a drive mode for displaying a live view. Since the image quality of the still image to be recorded is most important in the drive mode for picking up a still image, all the outputs from the effective pixels of the image pickup element are read. On the other hand, in the drive mode for displaying a so-called live view of displaying the image obtained by the image pickup element on the display section, which may typically be an LCD, on a real-time basis, the output of the image pickup element is partly thinned to feasibly display the picked up image on a real-time basis by reducing the time for reading out the output of the image pickup element and subsequently processing the image.
Meanwhile, it is known that the spectral sensitivity characteristics of the same image pickup element vary depending on the drive mode. For example, it is known that an NMOS-type image pickup element shows a stronger color mixing tendency in the drive mode for displaying a live view than in the drive mode for picking up a still image.
Under these circumstances, image pickup elements are required to show the same color reproducibility both when displaying a live view and when picking up a still image. For example, Jpn. Pat. Appln. Publication No. 2001-339734 discloses a technique of computationally determining the spectral characteristics at the time of an image pickup operation (comprehensive spectral characteristics) from the spectral characteristics stored in the memory of a unit (e.g., a lens unit or a image pickup unit) that can be removably fitted to the camera being used for the operation and the spectral characteristics that correspond to the image pickup condition of the camera main body and are stored in the memory in the camera main body. Then, the white balance correction value and the color-conversion value are computed according to the computationally determined comprehensive spectral characteristics.
To realize the same color reproducibility both for picking up a still image and for displaying a live view by means of the technique disclosed in Jpn. Pat. Appln. Publication No. 2001-339734, the spectral sensitivity characteristics of the image pickup element for the time of picking up a still image and the spectral sensitivity characteristics of the image pickup element for the time of displaying a live view are stored and the white balance correction value and the color-conversion value for the still image and those for displaying a live view are computed from the respective spectral sensitivity characteristics, the spectral radiance characteristic of the light source at the time of the image pickup operation, the spectral transmittance characteristic of the optical lens of the camera, the spectral reflectance characteristic of the target color and the RGB value of the target color. The process of white balance correction and that of color-conversion for displaying a live view are executed according to the white balance correction value and the color-conversion value at the time of displaying a live view in the mode of displaying a live view, whereas that processing for picking up a still image is executed according to the white balance correction value and the color-conversion value at the time of picking up a still image. With this arrangement, it is possible to obtain an image to be displayed in the drive mode for displaying a live view and an image picked up in the drive mode for picking up a still image with the same color reproducibility. In other words, the colors of the image displayed as live view agree with the colors of the still image that is picked and reproduced.